Polymer glass transition temperature manipulation via z/e hydrazone photoswitching

ABSTRACT

In an embodiment, the present disclosure pertains to a method of changing the glass transition temperature of a polymer. In some embodiments, the polymer includes at least one hydrazone-containing compound. In general, the methods of the present disclosure include one or more of the following steps of: (1) applying light to the polymer; and (2) thereby changing the glass transition temperature of the polymer. In another embodiment, the present disclosure pertains to a polymer having a light-adjustable glass transition temperature. In some embodiments, the polymer includes at least one hydrazone-containing compound.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/899,991, filed on Sep. 13, 2019. The entirety of theaforementioned application is incorporated herein by reference.

BACKGROUND

Various methods such as, for example, photomelting or photofluidization,can be used to manipulate healability and re-shapeability of polymers.For example, the use of ultraviolet light to induce trans→cisisomerization of polymer-containing azobenzenes has been used tore-shape polymers. However, there are general restrictions of theseapplications due to limitations of azobenzenes. For instance,azobenzenes have limited substrate penetration depth. Moreover, thethermal instability of the azobenzene cis isomer precludes thelocking-in of different glass transition temperature values. Variousembodiments of the present disclosure address the aforementionedlimitations.

SUMMARY

In an embodiment, the present disclosure pertains to a method ofchanging the glass transition temperature of a polymer. In someembodiments, the polymer includes at least one hydrazone-containingcompound. In general, the methods of the present disclosure include oneor more of the following steps of: (1) applying light to the polymer;and (2) changing the glass transition temperature of the polymer.

In another embodiment, the present disclosure pertains to a polymerhaving a light-adjustable glass transition temperature. In someembodiments, the polymer includes at least one hydrazone-containingcompound.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a method of changing the glass transition temperature(T_(g)) of a polymer according to an aspect of the present disclosure.

FIG. 2 depicts the generalized structure of a Z-hydrazone monomer, wherethe acrylate group may be tethered either at R₁ or R₂ positions, and Ymay be either t-butyl or H. The structure of hydrazone 6 is also shownin FIG. 2.

FIG. 3 illustrates differential scanning calorimetry (DSC) curves(second cycles) of different photostationary states (PSSs) of P9obtained by irradiation at various wavelengths of light.

DETAILED DESCRIPTION

It is to be understood that both the foregoing general description andthe following detailed description are illustrative and explanatory, andare not restrictive of the subject matter, as claimed. In thisapplication, the use of the singular includes the plural, the word “a”or “an” means “at least one”, and the use of “or” means “and/or”, unlessspecifically stated otherwise. Furthermore, the use of the term“including”, as well as other forms, such as “includes” and “included”,is not limiting. Also, terms such as “element” or “component” encompassboth elements or components comprising one unit and elements orcomponents that include more than one unit unless specifically statedotherwise.

The section headings used herein are for organizational purposes and arenot to be construed as limiting the subject matter described. Alldocuments, or portions of documents, cited in this application,including, but not limited to, patents, patent applications, articles,books, and treatises, are hereby expressly incorporated herein byreference in their entirety for any purpose. In the event that one ormore of the incorporated literature and similar materials defines a termin a manner that contradicts the definition of that term in thisapplication, this application controls.

The temperature at which a polymer transitions from a hard and glassystate into a soft rubbery one is termed the glass transition temperature(T_(g)). This physical property defines the function of a polymer,mechanical properties, how it can be applied, and whether it isre-proces sable and healable at ambient temperatures.

In most cases, the T_(g) of a polymer, and hence associated properties,cannot be changed once the polymer is made. However, there are ways toinfer healability and re-shapeability on polymers without having ambientT_(g) values. This can be achieved by exposing polymers to plasticizingsolvents or liquefying them by heating above their T_(g) values.

Alternatively, “photomelting” or “photofluidization” can be used toachieve this goal, though these processes are far less explored andunderstood. In both cases, light-induced translcis isomerization ofazobenzene associated with polymers is used to enable “flow” in thepolymer by realigning the azobenzene units and/or disruptingintramolecular interactions.

The aforementioned approaches are promising strategies for liquefyingpolymers as they rely on the high spatial and temporal resolution oflight, do not require additional components such as plasticizers towork, and can be used in various potential applications (e.g.,photolithography, fabrication of diffraction elements, self-healabledevices, and actuators). However, major restrictions to the generalapplication of the aforementioned approaches are limitations associatedwith the trans/cis isomerization of azobenzene, such as limitedsubstrate penetration depth and limited thermal stability of the cisisomer. Such limitations in turn preclude the locking-in of differentT_(g) values.

In sum, a need exists for more effective compositions and methods forpolymer glass transition temperature manipulation. Various embodimentsof the present disclosure address the aforementioned need.

In some embodiments, the present disclosure pertains to methods ofchanging the glass transition temperature (T_(g)) of a polymer thatincludes at least one hydrazone-containing compound. In some embodimentsillustrated in FIG. 1, the methods of the present disclosure includesteps of applying light to the polymer (step 10) and thereby changingthe glass transition temperature (T_(g)) of the polymer (step 12). Insome embodiments, the methods of the present disclosure can be repeateduntil desired results are achieved (e.g., the hydrazone-containingcompounds in the polymer transition from a Z state to an E state, thehydrazone-containing compounds in the polymer transition from an E stateto a Z state, or a desired T_(g) is reached).

In some embodiments, the present disclosure pertains to polymers thathave light-adjustable glass transition temperatures (T_(g)). In someembodiments, the polymers include at least one hydrazone-containingcompound. Additional embodiments of the present disclosure pertain tomethods of making the polymers of the present disclosure.

As set forth in more detail herein, the methods and polymers of thepresent disclosure can have numerous embodiments. For instance, themethods of changing the T_(g) of the polymers of the present disclosurecan utilize numerous polymers, hydrazone-containing compounds, lightsources, light application methods, and mechanisms of changing theT_(g). The methods of the present disclosure can also have variouseffects on the polymers of the present disclosure. Various methods mayalso be utilized to make the polymers of the present disclosure.Additionally, the polymers of the present disclosure may include varioushydrazone-containing compounds and T_(g) values.

Polymers

As set forth in further detail herein, the present disclosure canutilize various types of polymers. In some embodiments, the polymers ofthe present disclosure generally have a light-adjustable glasstransition temperature (T_(g)). In some embodiments, the polymers of thepresent disclosure include at least one hydrazone-containing compoundthat can be associated with the polymers in various manners. In someembodiments, the polymers of the present disclosure lack azobenzeneunits.

In some embodiments, the polymers of the present disclosure can include,without limitation, atactic polymers, syndiotactic polymers,homopolymers, heteropolymers, cyclopolymers, isotactic polymers, andcombinations thereof. In some embodiments, the polymers of the presentdisclosure can include, without limitation, biopolymers, inorganicpolymers, organic polymers, conductive polymers, copolymers,fluoropolymers, phenolic resins, polyanhydrides, polyketones,polyesters, polyethers, polyolefins (polyalkenes), rubbers, silicones,silicone rubbers, superabsorbent polymers, synthetic rubbers, vinylpolymers, and combinations thereof.

In some embodiments, the polymers of the present disclosure can include,without limitation, polyesters, polyamides, phenol-methanal plastics,polyurethanes, polycarbonates, and combinations thereof. In someembodiments, the polymers of the present disclosure can include, withoutlimitation, acrylate polymers, methyl acrylate polymers, andcombinations thereof.

In some embodiments, the polymers of the present disclosure can include,without limitation, polyethylene, polypropylene, polystyrene, poly(vinylchloride), polyisobutylene, poly(methyl acrylate), poly(methylmethacrylate), polytetrafluoroethylene, poly(acrylic acid),polyacrylamide, polyacrylonitrile, poly(hydroxyethyl methacrylate),poly(hydroxyethyl acrylate), and combinations thereof.

Hydrazone-Containing Compounds

Hydrazone-containing compounds generally refer to compounds that includeat least one hydrazone. The polymers of the present disclosure caninclude various types of hydrazone-containing compounds. For instance,in some embodiments, the at least one hydrazone in thehydrazone-containing compound is capable of transitioning from a Z stateto an E state upon exposure to light. In some embodiments, the at leastone hydrazone in the hydrazone-containing compound is capable oftransitioning from a Z state to an E state upon exposure to light.

In some embodiments, the hydrazone-containing compounds of the presentdisclosure have the following chemical configurations:

and combinations thereof.

In some embodiments, Y, R₁, and R₂ can each independently include,without limitation, H, alkyl groups, alkenyl groups, alkoxy groups, arylgroups, ketone groups, amine groups, amide groups, carboxyl groups,carboxylic acid groups, ester groups, thiol groups, sulfoxide groups,alcohol groups, alkyne groups, azide groups, the polymers of the presentdisclosure, and combinations thereof. In some embodiments, Y, R₁ and R₂can each independently include the polymers of the present disclosure.

In some embodiments, Y, R₁, and R₂ can each independently include,without limitation, CH₂CH₃, C(CH₃), (CH₂)₅CH₃, (CH₂)₇CH₃, (CH₂)₉CH₃,(CH₂)₁₁CH₃, (CH₂)₁₋₂₀ CH₃, t-butyl, n-hexyl, n-octyl, n-decyl,n-dodecyl,

and derivatives thereof. In some embodiments, n is an integer greaterthan or equal to 1.

In some embodiments, the hydrazone-containing compounds can include,without limitation:

derivatives thereof, and combinations thereof. In some embodiments, n isan integer greater than or equal to 1.

The hydrazone-containing compounds of the present disclosure can beassociated with the polymers of the present disclosure in variousmanners. For instance, in some embodiments, the hydrazone-containingcompounds of the present disclosure can be part of a side chain of thepolymer. In some embodiments, the hydrazone-containing compounds of thepresent disclosure are part of monomeric units of the polymers of thepresent disclosure. In some embodiments, the hydrazone-containingcompounds can be covalently embedded within a network of the polymer. Insome embodiments, the hydrazone-containing compounds can benon-covalently embedded within a network of the polymer.

Light

Various light sources may be applied to the polymers of the presentdisclosure. For instance, in some embodiments, the light is derived froma light source. In some embodiments, the light source includes, withoutlimitation, an arc lamp system, short-wave ultraviolet lamps,incandescent lamps, gas-discharge lamps, ultraviolet light emittingdiodes, ultraviolet lasers, tunable vacuum ultraviolet systems, naturallight, and combinations thereof.

Application of Light

Various methods may be utilized to apply light to the polymers of thepresent disclosure. For instance, in some embodiments, the applicationof light can be through irradiation.

In some embodiments, light is applied to the polymers of the presentdisclosure at various wavelengths. For example, in some embodiments,light is applied at wavelengths ranging from about 300 nm to about 500nm. In some embodiments, light is applied at a wavelength of about 340nm. In some embodiments, light is applied at a wavelength of about 365nm. In some embodiments, light is applied at a wavelength of about 375nm. In some embodiments, light is applied at a wavelength of about 394nm. In some embodiments, light is applied at a wavelength of about 410nm.

Changing of Polymer T_(g)

In some embodiments, the T_(g) of a polymer can be characterized as thetemperature at which the polymer transitions from a hard andnon-malleable state into a soft and malleable state. The application oflight can have various effects on the T_(g) of the polymers of thepresent disclosure.

For instance, in some embodiments, the application of light increasesthe T_(g) of the polymers of the present disclosure. In someembodiments, the increase in T_(g) results in the stiffening of thepolymer. In some embodiments, the increase in T_(g) is more than 5° C.In some embodiments, the increase in T_(g) is more than 10° C. In someembodiments, the increase in T_(g) is more than 15° C.

In some embodiments, the application of light decreases the T_(g) of thepolymers of the present disclosure. In some embodiments, the decrease inT_(g) results in the softening of the polymer. In some embodiments, thedecrease in T_(g) is more than 1° C. In some embodiments, the decreasein T_(g) is more than 5° C. In some embodiments, the decrease in T_(g)is more than 10° C. In some embodiments, the decrease in T_(g) is morethan 15° C.

Mechanisms of Changing Polymer T_(g)

Without being bound by theory, the polymers of the present disclosurecan have various mechanisms of T_(g) transition. For instance, in someembodiments, the change in T_(g) occurs through photo-isomerization. Insome embodiments, the hydrazone-containing compounds transition from a Zstate to an E state upon photo-isomerization. In some embodiments, thetransition from a Z state to an E state is characterized by a decreasein the Z/E isomer ratio.

In some embodiments, the hydrazone-containing compounds transition froman E state to a Z state upon photo-isomerization. In some embodiments,the transition from an E state to a Z state is characterized by anincrease in the Z/E isomer ratio.

Effects of Changing T_(g)

The changes of the T_(g) of the polymers of the present disclosure canresult in numerous effects. For instance, in some embodiments, the T_(g)change is permanent. In some embodiments, the T_(g) change iscontrollable as a function of light irradiation time, light wavelength,and combinations thereof. In some embodiments, the T_(g) change is theresult of a change in the ZIE isomer ratio of the hydrazone in thehydrazone-containing compound.

Methods of Making Polymers

Additional embodiments of the present disclosure pertain to methods ofmaking the polymers of the present disclosure. Such methods generallyinclude associating the hydrazone-containing compounds of the presentdisclosure with the polymers of the present disclosure.

In some embodiments, hydrazone-containing compounds can be associatedwith polymers by covalently linking the hydrazone-containing compoundswith the polymers. In some embodiments, hydrazone-containing compoundscan be associated with polymers by non-covalently associating thehydrazone-containing compounds with the polymers.

In some embodiments, the methods of making the polymers of the presentdisclosure can include polymerization of monomers to the polymers of thepresent disclosure in the presence of the hydrazone-containing compoundsof the present disclosure. In some embodiments, the hydrazone-containingcompounds of the present disclosure have a monomer group (e.g., anacrylate group) tethered at various positions in order to facilitate thepolymerization and formation of the polymers of the present disclosure.

Applications and Advantages

The present disclosure can have various advantages. For instance, insome embodiments, the methods of the present disclosure can be utilizedto manipulate the stiffness of the polymers of the present disclosure atvarious desired temperatures (e.g., ambient and higher temperatures)through light irradiation.

As such, the methods and polymers of the present disclosure can beutilized in various manners and for various purposes. For instance, insome embodiments, the methods and polymers of the present disclosure canbe utilized as healable and reconfigurable polymers for various uses. Insome embodiments, such uses can include, without limitation, utilizationof the polymers as medical implants, self-healable devices, actuators,or combinations thereof. In some embodiments, such uses can include theutilization of the methods of the present disclosure in photolithographyand fabrication of diffraction elements.

Additional Embodiments

Reference will now be made to more specific embodiments of the presentdisclosure and experimental results that provide support for suchembodiments. However, Applicants note that the disclosure below is forillustrative purposes only and is not intended to limit the scope of theclaimed subject matter in any way.

Example 1. Polymer Glass Transition Temperature Manipulation Via ZIEHydrazone Photoswitching

This Example describes polymer glass transition temperature manipulationvia Z/E hydrazone photoswitching.

The temperature at which a polymer transitions from a hard and glassystate into a soft rubbery one is termed the glass transition temperature(T_(g)). This physical property defines the function of a polymer,mechanical properties, how it can be applied, and whether it isre-processable and healable at ambient temperatures. In most cases, theT_(g) of a polymer, and hence associated properties, cannot be changedonce the polymer is made. There are ways though to infer healability andre-shapeability on polymers, without them necessarily having ambientT_(g) values. This can be achieved by exposing them to plasticizingsolvents or liquefying them by heating them above their T_(g) values.

Alternatively, “photomelting” or “photofluidization” can be used toachieve this goal. However, such processes are far less explored andunderstood.

In both cases, light-induced trans/cis isomerization of azobenzene (alight-switch of choice in these applications) is used to enable “flow”in the polymer by realigning the azobenzene units and/or disruptingintramolecular interactions. These are promising strategies forliquefying polymers as they rely on the high spatial and temporalresolution of light, do not require additional components such asplasticizers to work, and can be used in various potential applications(e.g., photolithography, fabrication of diffraction elements,self-healable devices, and actuators, etc.). What restricts the generalapplication of these approaches though are the limitations of theazobenzene. For example, the use of ultraviolet (UV) light (in mostcases) to induce trans→cis isomerization limits substrate penetrationdepth, and the thermal instability of the cis isomer precludes thelocking-in of different T_(g) values.

To address some of these issues, Applicants incorporated recentlydeveloped hydrazone photoswitches into polyacrylate and polymethacrylatepolymers as side chains, and studied the effect of photoisomerization onthe T_(g)s of the polymers. Applicants' hypothesis was that thebistability of these new switches will allow Applicants to lock-indifferent T_(g) values for the same polymer as a function of irradiationwavelength, i.e., the isomer Z/E ratio at the photostationary state(PSS). Moreover, Applicants anticipated that the negative photochromicnature of the hydrazone will allow Applicants to overcome thepenetration depth issue, which limits the photoreaction in azopolymersto the sample surface.

In this Example, Applicants report on the structure-property analysis ofhydrazone-containing polyacrylate and polymethacrylate polymers and showthat not only can Applicants lock different T_(g) values in thesesystems, but also that the change in T_(g) values increases uponphotoisomerization. This is an opposite trend from what is observed inazopolymers, where an order to disorder transition upon trans→cisisomerization lowers the T_(g) of the polymer, and which in certaincases induces a solid-to-liquid transition. With hydrazones on the otherhand, there is usually an order to (higher) order transition upon Z→Ephotoisomerization, which can explain why Applicants observe an increasein T_(g) (i.e., stiffening of the polymers within the window oftemperatures between the initial (Z-rich) T_(g) and final (E-rich)T_(g)).

Example 1.1. Synthesis

The hydrazone containing monomers 1-13 (FIG. 2), were synthesized in astraightforward manner in relatively high yields (50-99%) and werecharacterized using nuclear magnetic resonance (NMR) spectroscopy andmass spectrometry. The monomers were then each polymerized usingreversible addition-fragmentation chain-transfer (RAFT) conditions witha target degree of polymerization (X_(n)) of 150 in reasonable yields(41-85%). RAFT was chosen to control the polymer molecular weight whilesimultaneously mitigating dispersity.

Example 1.2. Thermal Analysis

Differential scanning calorimetry (DSC) was used to measure the glasstransition temperature of each polymer (Table 1) in both pristine(i.e., >99% Z) and photostationary states (i.e., E enriched at PSS₄₁₀).The PSS₄₁₀ was reached for each material by dissolving it in CD₂Cl₂ andirradiating with 410 nm light. Reaching PSS₄₁₀ was confirmed for eachproduct through ¹H NMR analysis, which revealed the formation of >94% Efor all polymers except for P6 which reaches 80% E at the PSS. PolymerP1, which Applicants will take as a baseline material for thepolymethacrylate polymers, displays a pristine T_(g) of 86° C. and anE-rich T_(g) of 103° C., resulting in a ΔT_(g) of +17° C. (Table 1).

This increase in T_(g) when switching from the thermodynamically morestable form (Z in this case) to the less stable form (E) isunprecedented in T_(g) switchable polymers. By lengthening the tetherbetween the hydrazone pendant and the methacrylate backbone, as in P2,Applicants observed a depression of the pristine T_(g). This is to beexpected since the system's rigidity is decreased though the longertether. Applicants also observed a diminished effect upon T_(g) whenswitching from Z to E-rich material (41 and 48° C., respectively)resulting in a ΔT_(g) of only +7° C. This result implies that thephotoswitch should be proximally close to the backbone to significantlymanipulate the T_(g).

When the ethyl ester in P1 was exchanged for a bulky t-butyl group, thepristine material's T_(g) increased to 98° C. while the substitution hadlittle effect on ΔT_(g) (+16° C.). The addition of the bulky t-butylgroup likely introduced more rigidity to the system throughintercalation, which ultimately elevated the T_(g) of both Z and E-richmaterials nearly equally. By moving the bulky t-butyl group to the rotorphenyl group in the hydrazone, the T_(g) of the Z-rich polymer wasfurther elevated to 107° C. However, this had an adverse effect onΔT_(g), which decreased to −1° C. Finally, P5 represents aregiochemically differentiated alternative to P1 where the hydrazone istethered to the backbone through an ester group (R₁). This change hadlittle effect on the pristine polymer's T_(g) (83° C.), but served tominimize the impact of photoswitching on the T_(g) of the E-richmaterial, resulting in a ΔT_(g) of only +4° C.

TABLE 1 Summary of the T_(g)S of P1-P13 before and after isomerization.T_(g) pristine T_(g) PSS₄₁₀ (Z rich) (E rich) ΔT_(g) (° C.) (° C.) (°C.) P1 86 103 +17 P2 41 48 +7 P3 98 114 +16 P4 107 106 −1 P5 83 87 +4 P672 69 -3 P7 68 79 +11 P8 64 73 +9 P9 75 97 +22 P10 33 42 +9 P11 28 42+14 P12 20 35 +15 P13 21 37 +16

Next, Applicants studied the effect of photoisomerization on the T_(g)of the polyacrylate polymers P6-P13. Applicants decided to shift topolyacrylate polymers, as in general it has lower T_(g) values and soApplicants speculated that this property will allow Applicants to inducea controllable rubber-to-glass phototransition, which is in oppositedirection to what is observed with azobenzene. Polymer P6, which is madefrom the simplest hydrazone having the acrylate attached at the estergroup position (R₁), has the lowest measured pristine and switched T_(g)so far in the series, as expected from the polyacrylate polymer. TheΔT_(g), however, is small and negative, which can be attributed to thelack of the second ester group in the molecule, and hence second H-bondthat rigidifies the system. Polymer P7 is the polyacrylate equivalent ofP1 and as expected (Table 1) has a lower pristine T_(g) value, andslightly lower ΔT_(g) value (11 vs. 17, respectively). To assess theinfluence of the position of the polymerizable unit on the T_(g)Applicants also studied P8 and P9. While the former exhibits slightlylower T_(g) and ΔT_(g) values compared to P7, the latter has a higherpristine T_(g) value, and intriguingly the largest ΔT_(g) in the series(+22° C.). This result indicates that there is better packing inpristine P9 relative to P7, and that the packing upon photoisomerizationis the best in the series.

Next, Applicants exchanged the ethyl group in the switch with a hexylone, to generate free volume that might lower the T_(g) value further,while maintaining the polymerization group at the para position tomaintain the large ΔT_(g) value. Applicants' hypothesis proved to bepartially correct as the T_(g) of pristine P10 went down to 33° C.,however, the ΔT_(g) dropped to +9° C. Applicants assume that thegenerated free volume lowers the difference in the packing efficiencybetween the two isomers. Nonetheless, this result is a step closer to apolymeric system having an ambient T_(g).

Next, Applicants elongated the alkyl chain further to octyl (P11), decyl(P12) and dodecyl (P13) in an effort to further lower the pristine T_(g)value, and indeed this is what Applicants obtained, with the latter twohaving ambient T_(g) values. Moreover, the ΔT_(g) value increasedslightly from P10 to −15° C., allowing for a better control over theproperties of the polymers. It also seems that Applicants reached thelimit of how low the alkyl chain length can push the T_(g) value, asboth P11 and P12 have almost the same value.

Next, and as a proof of principle, Applicants used P9 to show that notonly can Applicants manipulate the T_(g) value, but Applicants can alsolock it in at different values between 75 and 97° C. as a function ofwavelength-dependent PSS (FIG. 3). Applicants first measured the Z/Eisomer ratios at different photostationary states obtained after 340,365, 375, 394 and 410 nm light irradiation, using ¹H NMR spectroscopy.Then Applicants used these wavelengths to obtain different T_(g) valuesas measured by DSC. It can be seen that 4-7° C. steps can be obtainedwhen enriching the system with the E isomer by moving from PSS₃₆₅ toPSS₄₁₀. Each one of these steps can be locked in place, as evident bythe fact that no changes are observed in the DSC curves between thefirst and second heating cycles. This observation can be attributed tothe bistability of the hydrazones (i.e., half-lives in the range ofhundreds to thousands of years), which require prolonged heating at hightemperatures to initiate the E→Z thermal isomerization. Unfortunately,there is no direct way to quantify the obtained change in T_(g) as afunction of change in E/Z isomer ratio, and therefore it can beenvisioned that the higher the E ratio the higher the T_(g) value.

An exception appears to be when moving from pristine Z and PSS₃₄₀ wherethe Z ratio goes from >99% to 83%. It seems that not enough E isomer isaccumulated at this stage to affect the T_(g) of the system and so itremains at 75° C.

These results are in general very promising as they indicate thatApplicants can manipulate the T_(g) values of two families of polymersover a broad range, while maintaining large enough ΔT_(g) values thatare favorable for different types of applications. In most cases theT_(g) value of the polymers increases after photoirradiation, which iscontrary to what is obtained in azopolymers. This unique property is anadded benefit to these systems, as it stems from structural changes inthe hydrazone and not a random order/disorder transition as observed inthe azopolymers. This observation means that the T_(g) can be furthermanipulated in the future through structural modifications.

Moreover, Applicants showed that Applicants can use wavelength-dependentPSS to access and lock-in different T_(g) values for the same polymer.This property is not possible with azopolymers, even with ones that useazobenzene derivatives that have long thermal half-lives, as in mostcases the Z isomer is metastable, and quickly reverts to the E formunder ambient conditions, and more so upon heating during DSCmeasurements.

Without further elaboration, it is believed that one skilled in the artcan, using the description herein, utilize the present disclosure to itsfullest extent. The embodiments described herein are to be construed asillustrative and not as constraining the remainder of the disclosure inany way whatsoever. While the embodiments have been shown and described,many variations and modifications thereof can be made by one skilled inthe art without departing from the spirit and teachings of theinvention. Accordingly, the scope of protection is not limited by thedescription set out above, but is only limited by the claims, includingall equivalents of the subject matter of the claims. The disclosures ofall patents, patent applications and publications cited herein arehereby incorporated herein by reference, to the extent that they provideprocedural or other details consistent with and supplementary to thoseset forth herein.

What is claimed is:
 1. A method of changing the glass transitiontemperature (T_(g)) of a polymer, wherein the polymer comprises at leastone hydrazone-containing compound, and wherein the method comprises:applying light to the polymer, wherein the light changes the glasstransition temperature (T_(g)) of the polymer.
 2. The method of claim 1,wherein the polymer is selected from the group consisting of acrylatepolymers, methyl acrylate polymers, or combinations thereof.
 3. Themethod of claim 1, wherein the polymer is selected from the groupconsisting of polyethylene, polypropylene, polystyrene, poly(vinylchloride), polyisobutylene, poly(methyl acrylate), poly(methylmethacrylate), polytetrafluoroethylene, poly(acrylic acid),polyacrylamide, polyacrylonitrile, poly(hydroxyethyl methacrylate),poly(hydroxyethyl acrylate), or combinations thereof.
 4. The method ofclaim 1, wherein the hydrazone-containing compound is part of a sidechain of the polymer.
 5. The method of claim 1, wherein thehydrazone-containing compound comprises:

or combinations thereof.
 6. The method of claim 5, wherein Y, R₁ and R₂are each independently selected from the group consisting of H, alkylgroups, alkenyl groups, alkoxy groups, aryl groups, ketone groups, aminegroups, amide groups, carboxyl groups, carboxylic acid groups, estergroups, thiol groups, sulfoxide groups, alcohol groups, alkyne groups,azide groups, the polymer, or combinations thereof.
 7. The method ofclaim 5, wherein Y, R₁ and R₂ each independently comprises the polymer.8. The method of claim 5, wherein Y, R₁ and R₂ are each independentlyselected from the group consisting of CH₂CH₃, C(CH₃), (CH₂)₅CH₃,(CH₂)₇CH₃, (CH₂)₉CH₃, (CH₂)₁₁CH₃, (CH₂)₁₋₂₀CH₃, t-butyl, n-hexyl,n-octyl, n-decyl, n-dodecyl,

or derivatives thereof, wherein n is an integer of more than
 1. 9. Themethod of claim 1, wherein the hydrazone-containing compound is selectedfrom the group consisting of:

derivatives thereof, or combinations thereof, wherein n is an integer ofmore than
 1. 10. The method of claim 1, wherein the light is derivedfrom a light source selected from the group consisting of an arc lampsystem, short-wave ultraviolet lamps, incandescent lamps, gas-dischargelamps, ultraviolet light emitting diodes, ultraviolet lasers, tunablevacuum ultraviolet systems, natural light, or combinations thereof. 11.The method of claim 1, wherein the change in T_(g) occurs throughphoto-isomerization, and wherein the hydrazone in thehydrazone-containing compound transitions from a Z state to an E stateupon photoisomerization.
 12. The method of claim 1, wherein the changein T_(g) occurs through photo-isomerization, and wherein the hydrazonein the hydrazone-containing compound transitions from an E state to a Zstate upon photoisomerization.
 13. The method of claim 1, wherein theapplication of light increases T_(g), and wherein the increase in T_(g)results in stiffening of the polymer.
 14. The method of claim 1, whereinthe application of light decreases T_(g), and wherein the decrease inT_(g) results in softening of the polymer.
 15. A polymer comprising alight-adjustable glass transition temperature (T_(g)), wherein thepolymer comprises: at least one hydrazone-containing compound.
 16. Thepolymer of claim 15, wherein the polymer is selected from the groupconsisting of acrylate polymers, methyl acrylate polymers, polyethylene,polypropylene, polystyrene, poly(vinyl chloride), polyisobutylene,poly(methyl acrylate), poly(methyl methacrylate),polytetrafluoroethylene, poly(acrylic acid), polyacrylamide,polyacrylonitrile, poly(hydroxyethyl methacrylate), poly(hydroxyethylacrylate), or combinations thereof.
 17. The polymer of claim 15, whereinthe hydrazone-containing compound is part of a side chain of thepolymer.
 18. The polymer of claim 15, wherein the hydrazone-containingcompound comprises:

or combinations thereof.
 19. The polymer of claim 18, wherein Y, R₁ andR₂ are each independently selected from the group consisting of H, alkylgroups, alkenyl groups, alkoxy groups, aryl groups, ketone groups, aminegroups, amide groups, carboxyl groups, carboxylic acid groups, estergroups, thiol groups, sulfoxide groups, alcohol groups, alkyne groups,azide groups, the polymer, CH₂CH₃, C(CH₃), (CH₂)₅CH₃, (CH₂)₇CH₃,(CH₂)₉CH₃, (CH₂)₁₁CH₃, (CH₂)₁₋₂₀CH₃, t-butyl, n-hexyl, n-octyl, n-decyl,n-dodecyl,

or derivatives thereof, wherein n is an integer of more than 1.orcombinations thereof.
 20. The polymer of claim 18, wherein Y, R₁ and R₂each independently comprises the polymer.
 21. The polymer of claim 15,wherein the hydrazone-containing compound is selected from the groupconsisting of:

derivatives thereof, or combinations thereof, wherein n is an integer ofmore than 1.